1. Field of the Invention
This invention relates to a three-point coupling device for coupling a tractor to an implement, comprising two lower hitch arms which are articulted in an offset way at the rear end of the tractor on different sides of the longitudinal axis of the tractor and whose free ends have each been provided with a catching hook having a lockable catching jaw which is open towards the top, with each lower hitch arm, via a lifting bar, being connected to a lifting arm movable by the power drive of the tractor; and comprising an upper hitch arm whose one end is articulated at the rear end of the tractor above the lower hitch arms in the region of the longitudinal axis and whose other end has been provided with a catching hook comprising a lockable catching jaw which opens towards the bottom or top, with the catching hooks, for coupling purposes, being suitable for engaging, or being released from, the corresponding coupling points of the implement to be coupled.
2. Description of Prior Art
With such a three-point coupling device the lower steering arms are coupled to the lower articulation points of the implement by driving the tractor towards the implement and lifting the lower hitch arms after the tractor has reached a position where it is approximately close enough to the implement. To facilitate coupling, the lower hitch arms are provided with catching hooks which are described for example in DE PS No. 25 10 490 and 30 33 663. Alignment of the catching hooks is facilitated for example by a catching profile known from DE PS No. 35 06 670.
The connection between the upper arm, which is also provided with a catching hook, and the upper coupling point is effected manually by the tractor driver who, either by lifting the upper hitch arm or actuating the already coupled lower hitch arms, has to achieve a coupling position for the catching hook of the upper hitch arm relative to the articulation point of the implement in order, then, to lower the upper hitch arm by hand. Such an upper hitch arm is known from DE-PS No. 26 08 276 for example.
In this procedure the tractor driver has to bend backwards to be able to hold and align the upper hitch arm, whereas at the same time he has to handle the steering wheel with the other hand to align the tractor relative to the implement and move it into an advantageous coupling position.
This type of procedure is complicated and also exhausting.
Furthermore, there is a prior art three-point coupling device in the case of which the lower hitch arms and the upper hitch arm have been provided with a triangular frame designed to engage a frame attached to the implement (U.S. Pat. No. 3 299 979).
The frame represents an additional component which, furthermore, has to be removed when the tractor is to be used in conjunction with a trailer. Because such a frame has to accommodate tensile and load bearing forces, it has to be of a stable design and is difficult to handle.
It is therefore an object of the present invention to provide a three-point coupling device which is easy to handle, does not require any strength on the part of the driver nor any re-fitting at the tractor rear when changing from trailer operation to the use of a three-point coupling device and vice versa.